Solutions of acrylonitrile polymers



Patented Apr. 11, 1950 SOLUTIONS OF ACRYLONITRILE POLYMERS Harry W. Coover, Theodore E. Stanin, and Joseph B. Dickey, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application September 16, 1948. Serial No. 49,655

Claims. (Cl. 260-323) This invention relates to solutions of acrylonitrile polymers and to a process for preparing such solutions.

It is known that solutions of polymers of acrylonitrile can be prepared by dissolving such polymers in various organic solvents or in aqueous solutions oi certain inorganic metal salts. These solutions have been found to be readily adaptable for spinning into fibers or in the manufacture of film. Since the metal salts have a tendency to deposit on the filaments during the spinning operation, and removal thereof during the passage 01' the filaments through the spinning bath leaves numerous voids or weak spots in the fibers, metal salts have not proved to be entirely satisfactory in the preparation of synthetic fibers. Difilculties are also encountered when organic solvents are used in the spinning of fibers from solutions of polymers of acrylonitrile. Yet particles frequently form, thus either clogging the spinnerets or giving a fiber of low tensile strength. Also the color of the fibers spun from many of the solvents heretofore used does not meet the standards demanded oi. a product in a competitive market.

Houtz U. S. Patent 2,404,713, dated July 23, 1946, and Latham U. S. Patent 2,404,714, dated July 23, 1946, describe a process for preparing solutions of polymers of acrylonitrile suitable for spinning into fibers which comprises dissolving the polymer in an organic compound containing a O CH: JLN

C Ha group, e. g., N,N-dimethylformamide. These solvents provide a convenient medium from which fibers can be spun, however, there is some tendency for the polymers containing acrylonitrile to ball" or form large gel particles therein. To overcome this difficulty, it has been proposed to add gaseous anhydrides to the cooled solvent containing the polymer to obtain a uniform dispersion of the polymer. in the vehicle, and then gradually warm the dispersion to a temperature of ION-130 C., while solution is effected and the gaseous anhydride is expelled from the solution (Finzel U. S. Patent 2,404,728, dated July 23, 1946).

Despite the improvements which have been realized in the art, white, lustrous fibers have not heretofore been obtainable from solutions oi polymers of acrylonitrile, nor have the solutions of the polymers been colorless, clear and gel-free to the degree necessary for a commercial product.

It is an object of this invention to provide substantially clear, colorless and gel-free solutions of polymers of acrylonitrile. Another object is to provide a process for obtaining such solutions. Still another object is to provide white, lustrous fibers from such solutions and a process for preparing such fibers. Other objects will become apparent from a consideration of the following description and examples.

According to our invention we accomplish the above objects by intermixing or commingling a polymer of acrylonitrile containing in'the polymer molecule at least per cent by weight of acrylonitrile with N,N-dimethylformamide or N,N-dimethylacetamide, in the presence of certain organic acids. The solutions so obtained are substantially water-clear and colorless, and are in addition substantially free of gel particles. Fi-

bers spun from solutions prepared according to our invention are lustrous and white, and of uniform strength or tenacity.

As organic acids we can use oxalic acid, acetic acid, trifluoroacetic acid, alkane sulfonic acids, aromatic sulfcnic acids, alkyl phosphoric and phosphorous acids, alkane phosphonic acids and alkene sulfonic acids. Typical alkane suli'onic acids include methanesulfonic, ethanesulfonic. propane-l-sulfonic, propane-Z-sulionic, n-butane-l-sulfonic, isobutane 1 sulfonic, sulio-.

acetic, p-hydroxy sulfonic, etc. acids (e. g. alkane sulfonic acids containing from 1 to 4 carbon atoms). Typical aromatic sulfonic acids in clude benzenesulfonic, p-toluenesulfonic, o-toluenesulfonic, m-benzenedisulfonic, 1,3,5-benzenetrisulfonic, etc. acids (e. g. a sulfonic acid of the benzene series). Other useful aromatic sulfonic acids include naphthalene u. sulicnic, naphthalene-fl-sulfonic, 1,5 naphthalenedisulfoni c, 2,6-naphthalenedisulfonic, etc., acids (e. g. a sulfonic acid of the naphthalene series). Typical alkyl phosphoric acids include monomethyl acid orthophosphatc, monoethyl acid orthophosphatc, mono-n-propyl acid orthophosphatc, monoisopropyl acid orthophosphate, mono-nbutyl acid orthophosphatc, monoisoamyl acid orthophosphatc, mono-n-octyl acid orthophos- 3 phate, mono-n-capryl acid orthophosphate, dimethyl acid orthophosphate, diethyl acid orthophosphate, ethyl isoamyl acid orthophosphate, ethyl n-octyl acid orthophosphate, ethyl n-capryl acid orthophosphate, di-n-butyl acid orthophosphate, n-butyl n-amyl acid orthophosphate, dimethyl acid pyrophosphate, diethyl acid pyrophosphate, di-n-propyl acid pyrophosphate, diisoproyl acid pyrophosphate, di-n-butyl acid pyrophosphate, diisoamyl acid pyrophosphate, di-n-octyl acid 'pyrophosphate, di-n-capryl acid pyrophosphate, etc. (See Alder and Woodstock "Chem. Ind. vol. II (1942), pg. 516.) Typical alkyl phosphorous acids include: monomethyl acid phosphite, monoethyl acid phosphite, monon-propyl acid phosphite, monoisopropyl acid phosphite, monoisobutyl acid phosphite, monoisoarnyl acid phosphite, dimethyl acid phosphite, diethyl acid phosphite, di-n-propyl acid phosphite, diisopropyl acid phosphite, di-n-butyl acid phosphite, diisobutyl acid phosphite, monoethyl acid hypophosphite, monoisobutyl acid hypophosphite, etc. Alkyl phosphoric and phosphorous acids (1. e. alkyl acid esters of acids of phosphorus) containing from 1 to 10 carbon atoms in the alkyl group have been found to be especially useful. Alkyl acid esters of acids of phosphorous containing from 1 to 5 atoms in the alkyl group constitute a preferred class. Typical alkane phosphonic acids include methane phosphonic, ethane phosphonic, n-propane phosphonic, isobutane phosphonic (isobutyl phosphonic), isoamyl phosphonic (isoamyl phosphonic), etc. acids (e. g. alkane phosphonic acids containing from 1 to 5 carbon atoms). Typical alkene phosphonic acids include: vinyl phosphonic, propene 2 phosphonic, a-phenylvinyl phosphonic, etc. acids (e. g. an afl-unsaturated, alkene phosphonic acid containing from 2 to 8 carbon atoms in the alkene group). Alkene phosphonic acids useful in practicing our invention are described in U. S. Patent 2,365,466, dated December 19, 1944. The advantages obtainedwith one or more of the above acids do not extend to organic acids generally we have found. For example, succinic, adipic, trichloroacetic, propionic, etc. acids do not provide the improvements which have been observed when the acids enumerated above are used.

The quantity of organic acid used varies and is generally a function of the particular acid employed. For the purposes of our invention we have found that from 0.1 to 5.0 per cent by weight, based on the weight of solvent, of acid is adequate. Larger or smaller quantities of acid can be used, although there is ordinarily no advantage in using amounts other than those indicated above. More than one acid (e. g. from 1 to 3) can be used at one time in preparing the solutions of our invention.

Advantageously we can effect solution of the polymers of acrylonitrile by applying a small amount of heat to the mixture of the acid, polymers and solvent. Since the acids used in our invention increase the dissolving power of the solvents to such a marked degree, it is not essential that the mixture be heated. Heat does serve to shorten the time required to effect solution. Care should be taken not to heat the mixture for prolonged periods of time, since heating lowers the color characteristic of fibers spun from heated solutions. The effect of prolonged heating on the solutions obtained according to the process of our invention is not as deleterious as that which results when solutions containing no acid are so heated. In order to obtain uniform solutions according to methods heretofore employed, the dispersion of polymer has to be subjected to high temperatures tor a time. This heating caused a diminution in desirable color properties in the solution, which are passed along during the spinning to the fibers formed. This heating can be largely or entirely avoided in our invention, however, thus providing fibers which are white and lustrous.

The inorganic gaseousanhydrides previously added to N,N-dimethylformamide were for the purpose of reducing the dissolving power of this solvent for the polymers of acrylonitrile, so that a dispersion could be obtained. The acids used in this invention are in contradistinction thereto for the purpose of increasing this dissolving power of the solvent for the polymer. Whereas the polymers used according to the older, less efllcacious methods had to be ground to minute particle size, the polymer used in this invention can be 20-mesh size or larger, with little or no apparent tendency to balling or the formation of gel particles. The solutions obtained in our invention are more stable than those obtained heretofore and show less tendency to gel. or develop color on standing.

The amount of polymer dispersed in the solvent can be varied depending on the intended use of the polymer solution and the molecular weight of the polymer, 1. e. larger quantities of the lower molecular weight polymers must be added to give a viscosity comparable to that obtained with a given amount of a higher molecular weight polymer. Although our invention is not to be limited thereby, generally our solutions can contain from about 2 to 25 per cent by weight of the polymer. based on the weight of the solvent. The molecular weight of the polymers used herein vary from about 50,000 to 500,000, although polymers having a molecular weight as low as 25,000 or as high as 750,000 can be used to advantage.

In our applications Ser. No. 49,651, Ser. No. 49,652, and Ser. No. 49,653, all filed on even date herewith, we have described methods for preparing polymers of acrylonitrile having improved solubility characteristics, and whose solutions can be spun into white, lustrous fibers, comprising polymerizing acrylonitrile in the presence of a persulfate polymerization catalyst (e. g. ammonium persulfate, etc.), a water-soluble, sulfurcontaining catalyst activator (e. g. sodium bisulfite, etc.) and certain types of acids, both inorganic and organic. Whereas the methods described in our copending applications provide improvements in the properties of acrylonitrile polymers, solutions of such polymers, and fibers prepared therefrom, and the present invention provides a convenient and efficacious method for preparing water-clear, gel-free solutions and white, lustrous fibers from po y P p cording to prior art methods, we have found that the present invention provides solutions of polymers of acrylonitrile, and fibers prepared therefrom, having even more markedly improved properties when the solutions and fibers prepared according to the process described herein are obtained from polymers of acrylonitrile prepared according to the processes described in our applications Ser. No. 49,651, Ser. No. 49,652 and Ser. No. 49,653. That is to say, by applying the improved process of this invention to the improved method for preparing polymers oi acrylonitrile, described 76 in our copending applications, solutions and fibers 8 of polymers of acrylonitrile of particularly outstanding properties. can be obtained.

Instead'oi? employing the acids themselves in our processes, .we can form the acid in situ, as

Solutions of the polymers obtained in the above examples were prepared by dispersing 1.0 g. of the polymer in 20 g. of N,N-dimethylformamide,

, adding a quantity of acid in the amount given for m'g g i of 2: acid I in the table below, and stirring until solution fi g lfg ggfi i 33 g z g xzig 2 2;; was effected. The transmission of light by the with the anhydride to form the free acid. This mums polymers a measured The method of procedure 818 0 serves to dehydrate the amount of transmissioniproved to be a reliable solvent toasubstantial degree, thus increasing the means for measuring the extent of solution and dissolving power of the solvent for the polymm the detection of any irregularities present. The Acetic. hydride has been found to provide an blue light transmission was particularly a useful especially useful means for forming aceglc acid method for illustrating solution properties, since in situ, if water is present in the solvent. \blue light wa more hi h y sorbed in a dis- The following examples will illustrate more colored solution than the other colors of the fully the manner whereby we practice our invenspectrum. The results are given in the following tion. table:

Table I l Transmission, per cent rfi r ol Acid or fjffig Ex- Anhydride g g I ample n 3 r e Blue Green Orange Red Violet green Per crnl e2 71 e9 44 2 4 5 4 3' a 1 85 so so as so so 1 70 19 as so as so 2e- 51 7e 15 51 e0 1 49 70 7s 7s 70 11 21 1 45 so c2 s1 s2 s5 s4 2 94 m 95 9s 05 04 2 70 79 s3 s4 as 81 was mea sured Based on the weight of solvent used.

EXAMPLE 1 10.0 g. of freshly distilled acrylonitrile, 1 cc. of 10 per cent hydrogen peroxide and 1 cc. of 6N sulfuric acid were added to 90 cc. of distilled water in which 0.2 g. of FeSO4.'7HzO had been dissolved.

- Polymerization began almost immediately as evidenced by the formation 'of a fine, powdery precipitate. The polymerization was complete in 3 to 4 hours at room temperature. The polymer was filtered oil, washed free of acid and iron with distilled water and dried.

EXAMPLE2 8.0 g. of freshly distilled acrylonitrlle, 2.0 g. of acrylamide and 1 cc. of 10 per cent hydrogen peroxide were added to 90 cc. of distilled water. The mixture was heated at C. for 24 hours, and the polymer which had precipitated was filtered off. washed with distilled water and dried.

EXAMPLE 3 10.0 g. of acrylonitrile and 0.02 g. of benzoyl peroxide were added to a solution of 25 cc. of glacial acetic acid and 25 cc. of N,N-dimethylformamide. The mixture was then heated at 60 C. for 24 hours. The polymer was filtered oil, washed with distilled water and dried.

EXANIPLE4 The above measurements were all based on the transmission of pure N,N dimethylformamide which was set at per cent. It can thus be seen that the addition of a small quantity of one of the acids (or anhydrides) set forth above produces a beneficial effect upon the polymer solutions. While heating the solution causes a reduction in the transmission of light, both in the case of the solution containing no acid and in the case of solutions containing an acid, the eiTect is much greater in the case of the solutions which contain no added acid, further lowering the light transmission of the solutions whose transmission prior to heating leaves much to be desired.

Heating also causes the solutions containing no added acid to gel in a relatively short period of time as shown in the table below. Since heat is generally used to shorten the time required to eilect solution of the polymers, it can be seen that the disadvantages caused through the use of heat presents a formidable problem both in the spinning operation of solutions of polymers into fibers because of the accelerated formation of gel particles, and the obtention of white,

lustrous fibers from solu ions subjected to the influences of heat. Solutionsof the polymers obtained in the above examples were'jprepared by dispersing 2.0 g. of the polymer in 20 g. of N,N-dimethylforrramide, adding an acid (or an.- hydride) in the amount given in the table below,

and stirring at room temperature until solution 1 was eiTeced. The solutions were then heated at C., and the time required for the solution to gel was observed. The observed time is given as the gel-time.

31?? i ?b'ioiha due to the eccentricity oi the polymer sol a t io nl t hz ge l l ing times v'ary'ina slightly from one batch of polymer to another. From the data given above it can be seen that the presence of an acid in the solution serves to stabilize the solution against gelling to an extent not heretofore obtainable.

32 g. of sulfuric acid (sp. grav. 1.84) and 86.7 g. of a 80 per cent aqueous solution of hydrogen peroxide were dissolved in liters of distilled water, and the mixture was degassed by refluxing at reduced pressure (20 mm.). While stirring the solution 1000 cc. of freshly distilled acrylonitrile were added. About 300 cc. of the acrylonitrile remained undissolved. The air in the reaction vessel was displaced by passing in gaseous nitrogen, and 34 g. of crystalline green ferrous sulfate (FeSOa'H-IzO) The reaction mixture was stirred intermittently as the polymer formed to dissolve the acrylonitrile monomer which remained undissolved. After 16 hours, the reaction mixture was filtered, and the filter cake was washed free of acid and iron. After drying, there were obtained 790 g. of polymer.

Several 0.1 g. portions of the polymer obtained in Example 5 were suspended in 10 cc. portions of N,N-dimethylformamide to give a 1 per cent solution of the polymer. 0.1 g. of the acids given in the table was added to the suspensions, which were stirred at room temperature. The transmission of blue light of the various solutions was then measured, the results of which are given in the following table:

Table III Transmission of Blue Acid Used Light Pa cent None Benuneeuiionie.. 'lolueneeulionien e ic e.

e III ar-Phenylvinyl Phos honie. Monoisoam lAcid bosphate... Diisoamyl cid Pyrophosphate acids set forth above can also be used in molecularly equivalent amounts for the acids illustrated. For example, methane phosphonic acid, in a molecularly equivalent amount, can replace the monoisoamyl acid phosphate used in Example 5. In a similar manner isopentane phosphonic (isoamyl phosphonic) acid can be employed.

while our invention has been described in detail above with particular reference to N,N-dimethylformamide as the solvent for the polymers of acrylonitrile, it is to be understood that N,N- dimethylacetamide can likewise be used to advantage. In order to use N,N-dimethylacetamide according to the present invention, the polymers of acrylonitrile must be prepared in manner described in our copending applications Ser. No. 49,651, Ser. No. 49,052 or Ser. No. 49,653, all filed on even date herewith. As described fully in those applications, polymers of acrylonitrile prepared in a manner other than the therein described methods (1. e. polymerizing the acrylonitrile in the presence of a persulfate polymerization catalyst. a water-soluble, inorganic sulfur-containing catalyst activation and one of the specified acids) fail to give solutions of the polymers which are suitable for spinning into fibers.

Although our invention has been found to'be especially useful in the preparation of solutions of the homopolymer of acrylonitrile, solutions of interpolymers of acrylonitrile with other interpolymerizable compounds, e. g. acrylic acid, acrylamide, ethyl acrylate, vinyl acetate, vinyl chloride, styrene, etc. can also be prepared. The interpolymers used should generally contain at least per cent by weight of acrylonitrile in the polymer molecule, since polymers containing less than this amount melt at too low temperatures to warrant their use in the preparation of commercial products, such as fibers or yarns. Generally from 6 to 9 per cent by weight of the other polymerizable material in the interpolymer is adequate for the purposes of our invention. Interpolymers, containing less than 80 per cent by weight of acrylonitrile in the polymer molecule (e. g. from 70 to 75 per cent) also can be advantageously utilized in the preparation of our polymer solution. These interpolymers are useful where an unusually high melting polymer is not required, as for example, in the preparation of films or sheets.

Although the reasons for the unexpected behavior and properties of the solutions of our invention are not fully understood, it appears that, at least in part, these phenomena are associated with a reduction in alkalinity of the solvent. Hydrocyanic acid is apparently released from the polymer under strongly alkaline conditions thus causing discoloration of the solutions. The fol lowing are pH measurements which were made on pure N,N dimethylformamide, N,N dimethylacetamide, and on mixtures of these solvents with various acids or anhydrides:

DMF +l7 Acetic Acid DMF +1 0 Acetic Anhydride.. DMF+27 Oxalic Acid DMF+ a Acetic Acid l N. N-dimethyliormamide. N, N-dimethylaoetamide.

The reduction in pH does have a beneficial effect on the polymer solutions in some instances, however, as has been pointed out above, not all organic acids give improved polymer solutions.

From the foregoing description and examples, it can be seen that the objects of our invention have been accomplished, and the art is provided with a convenient means for producing substantially water-solutions of polymers of acrylonitrile, which can be spun into fibers, or cast into sheets or films.

What we claim as our invention and desire secured by Letters Patent of the United States is: 1. As a new composition of matter, a polymer of acrylonitrile containing in the polymer molecule at least 80 per cent by weight of acrylonitrile, N,N-dimethylformamide and from 0.1 to 6.0 per cent by weight, based on the weight of the N,N-dimethylformamide, of an organic compound selected from the group consisting of oxalic acid, acetic acid, acetic anhydride, trifluoroacetic acid, aikane sulfonic acids, aromatic the polymer molecule at least 80 per cent by weight of acrylonitrile dissolved in N,N-dimethyliormamide containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,N- dimethylformamide, of an organic compound selected from the group consisting of oxalic acid, acetic acid, acetic anhydride, trifluoroacetic acid, alkane sulionic acids, aromatic sultonic acids, alkyl acid esters of acids of phosphorus, alkane phosphonic acids and alkene phosphonic acids. I 3. A polymer of acrylonitrile containing at least 80 per cent by weight of acrylonitrile in the polymer molecule dissolved in N,N-dimethyiiormamide containing from 0.1 to 5.0per cent by weight, based on the weight of the N,N-dimethyliormamide, of an alkane sulfonic acid containing from 1 to 4 carbon atoms.

4. A polymer of acrylonitrile containing at least 80 per cent by weight of acrylonitrile in the polymer molecule dissolved in N,N-dimethyliormamide containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,N-dimethylformamide, of a sulfonic acid of the benzene series. 5. A polymer of acrylonitrile containing at least 80 per cent by weight of acrylonitrile in the polymer molecule dissolved in N,N-dimethylformamide containin from 0.1 to 5.0 per cent by weight, based on the weight of the N,N-dimethylformamide, of an alkyl acid ester of an oxygen acid of phosphorus containing from 1 to 10 carbon atoms in the alkyl group.

6. A polymer of acrylonitrile containing at least 80 per cent by weight of acrylonitrile in the polymer molecule dissolved in N,N-dimethylformamide containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,N- dimethyliormamide, of ethanesulfonic acid.

'l. A polymer of acrylonitrile containing at least 80 per cent by weight of acrylonitrile in the polymer molecule dissolved in N,N-dimethyliormamide containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,N-dimethyliormamide, of benzenesultonic acid.

8. A polymer of acrylonitrile containing at least 80 per cent by weight ofacrylonitrile in the polymer molecule dissolved in N,N-dimethylformamide containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,N- dimethyliormamide, of an ,alkyl acid ester of ortho-phosphoric acid containing from 1 to 10 carbon atoms in the alkyl group.

9. A polymer of acrylonitrile containing at least 80 per cent by weight of acrylonitrile in the polymer molecule dissolved in N,N-dimethylformamide containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,N-dimethylformamide, of monoisoamyl acid orthophosphate.

10. A homopolymer of acrylonitrile dissolved in N,N-dimethylformamide containing from 0.1 to 5.0 per cent by'weight, based on the weight of the N,N-dimethylforma-mide, of an alkane sulfonic acid containing from 1 to 4 carbon atoms.

11. A homopolymer of acrylonitrile dissolved in N,N-dimethyliormamide containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,N-dimethylformamide, of a sulfonic acid of the benzene series.

12. A homopolymer of acrylonitrile dissolved in N,N-dimethylformamide containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,N-dimethylformamide, of an alkyl acid ester of an oxygen acid of phosphorus.

13. A homopolymer of acrylonitrile dissolved in N,N-dimethylformamide containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,N-dimethylformamide, of ethanesulionic acid.

14. A homopolymer of acrylonitrile dissolved in N,N-dimethylformamide containing from 0.1

to 5.0 per cent by weight, based on the weight a REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Finzel July 23, 1946 Number Certificate of Correction Patent No. 2,503,245 April 11, 1950 HARRY W. COOVER ET AL. It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 6, in the first footnote under Table I, first line thereof, for 100 0. read 110 0.;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 11th day of July, A. D. 1950.

THOMAS F. MURPHY,

Assistant Uommim'oner of Patents. 

1. AS A NEW COMPOSITION OF MATTER, A POLYMER OF ACRYLONITRILE CONTAINING IN THE POLYMER MOLECULE AT LEAST 80 PER CENT BY WEIGHT OF ACRYLONITRILE, N,N-DIMETHYLFORMAMIDE AND FROM 0.1 TO 5.0 PER CENT BY WEIGHT, BASED ON THE WEIGHT OF THE N,N-DIMETHYLFORMAMIDE, OF AN ORGANIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF OXALIC ACID, ACETIC ACID, ACETIC ANHYDRIDE, TRIFLUOROACETIC ACID, ALKANE SULFONIC ACIDS, AROMATIC SULFONIC ACIDS, ALKYL ACID ESTERS OF ACIDS OF PHOSPHORUS, ALKANE PHOSPHONIC ACIDS AND ALKENE PHOSPHONIC ACIDS. 